1. Field of the Invention
The present invention relates to an internal combustion engine provided with an exhaust gas purifying catalyst, and more specifically, to a start control device and a start control method, capable of ensuring early activation of the exhaust gas purifying catalyst by ignition timing retardation in a cold start mode and improved fuel combustibility.
2. Description of the Related Art
An air quantity control device for an internal combustion engine is described in Jpn. Pat. Appln. KOKAI Publication No. 6-101456. In this prior art example, a lag in the necessary ignition timing for early activation of a catalyst is calculated based on a driving condition of the engine, and the basic ignition timing is modified in accordance with this lag. Thereupon, the exhaust gas temperature increases, so that increase of the catalyst temperature is accelerated. At the same time, the quantity of intake air is increased for correction, depending on the opening of a throttle valve or the combination of the lag and the intake air quantity. Thus, the torque produced by an internal combustion engine can be kept at the same level as in the case where the ignition timing is not retarded.
In the prior art example described above, however, the opening of the throttle valve increases quickly in a cold start mode of the engine, so that the negative pressure in a intake pipe falls. If a fuel with relatively low volatility is used, therefore, it is more difficult for the fuel to evaporate. As a consequence, the air-fuel ratio temporarily becomes overlean, as indicated by broken line i in FIG. 3, so that combustion may possibly be destabilized. An internal combustion engine in which the air-fuel ratio is leaned out to ensure early increase of catalyst temperature, in particular, is considerably influenced by overleaning.